Physcis 4

Electrostatic effects are cause by the transfer of electrons. A positevely charged object lacks electrons and a negetively charged objects has extra electrons. There are two kinds of electric charge which are positve and negetive charges. like charges repel and unlike charges attract.

power = voltage + current.

resistance = voltage/current.

Longer and thinner wires have more resistance.

Ultrasound is sound above 20000 Hz which is a higher frequency than human can hear. Ultrasound have medical uses whic includes scans to see inside the body, messuring the rates of blood flow and breking up kidney stones. Longitudinal waves moves back and forth and the vibration is along the same direction as the direction of travel. Transverse waves moves up and down and the vibrations are at right angles to the direction of travel. Wavelength is the distance occupied by one complete wave. Wavelength= v/f.

Gamma rays are given out from the nucleus of certain radioactive materials. X-rays are made by firing high speed electrons at metal targets.

Fission is the splitting up of a large nucleus, it is currently used to generate electricity and it also leads to chain reaction which must be carefully controlled. Fuision is joining together of smaller nuclei.

The half-life is the average time for half of the nuclei to presnt to decay.

The medical use of radioactivity includes treating cancer. Only Beta and Gamma radiation can pass through skin, Alpha radiation is most widely used as it is the most penetrating.